Secret telephone system



Juy 2L 3925. LSQQEQ L. ESPENSCHIED SECRET TELE PHONE SYSTEM Original Filed Jan. S 1920 Sfheets-Sheet l Juiy 2E, E925.

L. EsPENSce-imm SECRET TELEPHONE SYSTEM Original Filed Jan. E 1920 5 Sheets-Sheet INVEN TQR. limfw A TTORNEY July 2l, E925.

L. ESPENSCHIED SECRET TELEPHONE SYSTEM Original Filed Jan. dggo 3 Sheets-Sheet 5 yBY .v ATTORNEY @hit-T59 IND TELEGRAPH CJMPANY, A CEPEATIN 0F NEW YORK.

snean'r aanneemt: ssamm.,

.Application med Januarygrtw, Serial No. 3501?@ Renewed May 115, im.

To all whom it may concern:

-Be it known that I, 'LLoYuEsPENsoEmn residing at Queens, inthe couutyf of Queens and State of New York, have. invented certain Improvements in Secret Telephone Sys# tems', of which the :following is a specifica tion. l

This invention' relates to transmission sysytenis 'and more particularly to a method of restoringlgt.

and 'means tor providingA secrecy in the transmission Kof messages over such systems. In general/it is the objectfl of the invention to provides systemof communication over which messages, such as telephonie messages, may be transmitted in such a manner that it will be practically impossible for unauthorized persons who might have access to the' mediumthrougli orover which the messages are transmitted to obtain .the information contained tlierein. It is 'furthermore a feature of the arran ements ofthe invention that ,they are app icable both to systems of communication employing'metallic conductor as the medium oftransmission and to radi systems. Other objects and features of 'the invention will appear more fully from the detailed description herein- .after given. f Y l v `The method of operation of the arrangements of thisinvention consists in'separat-` l ing by-selective circuits the normal telephone' frequency band into a plurality of subbands and of altering the normal frequency relationbetween these sub-bands and transmitting the frequency-bands in such altered relation, thereby rendering the transmission unintelligible toordinary instruments. At

- the receiving end of the system, the normal frequency relation between these sub-bands is restored, and the normal telephone frequency band is then received in the .usual manner.

' The invention may be more fully understood from the following-description together with the accompanying drawing in the Figures 1, ,2, 3, 4 and 5 of -which are illustrated arra gements embodying the 1n vention. In /Fingg is illustrated a translating station in a transmission system employing metallic conductors, including both sending and receiving apparatus for altering the normal frequency relation of the lsub-bandsV of the out oing message currents and for ie normal 'frequency relation of the sub ands Aof the Vincoming currents.

.shown schematically tion ofthe Aselective circuits of the vfrequency applicable to a radio system. ln Fi 3 and 4 are" graphic "representations o the methods of altering the normal fre uency relation existing between the sub-bands.

' .Referring tok Fig.- 3, a graphic representaordinary telephonie or voice tirev quen'cy band is illustrated, which baud ein. tends approximately from 200 'to 2000'cycles. This telephone band is. divided up into a plurality of sub-bands, which subdoands .are then juxtaposed in the original telephone frequency band. The breaking up ofthe original telephone 'bandds accomplished by band iilter type; the juxtaposing or shiiftin isl accomplished by -modi bands as thus rearranged in the requenc scale are combined upon a common circuit and transmitted in their reassigned position.

ation. The 'subi .tnot'n asrnuscnmn, or come, naw wenn, assiettes. To numerosi@ rsnnrnoim of the sub-bands 515 There is thus made available for transmist sion a n ew` frequency spectrum with thel colorsI shifted, as it were, but occupying no greater Aoverall range of frequencies than 'the original'band.

spectrum? is. transmitted to 'the distant receiver as theori'ginal fr' uency band ofapproximately 2000 cycles, t at is,l over an ordinary telephone circuit, or else, may be transmitted atea hi her carrier frelquency by heingmodulate upon a carrier current in the usual way., After modulation, lthe 'carrier channel may be transmitted either by wire or.1adio..-"i`liie new and artificial frequency spectrum will be unintel- .ligible to ordinary receiving instruments and accordiiiglyy secrecy may be provided for in' transmittin messages with the above described met od. A

In the -arrangement illustrated in Fi 3 the voice frequency'band is divided up into three equalsub-bands, such as ,.B, and C, l

of 600 cycles each. Sub-band A, extending from 200 to 800 cycles, is selected out by p vmeans of a band lilter, is modulated by being beaten b a carrier-current of 1200 cycles, and oft e resultant frequency bands produced thereby the suml term of the modulation is selected out by a band' filter, thus shifting the 200 to 800 cycle band to its new position in the broader range, namely, 1400 to 2000 cyclesT Sub-bandB, extending from -This new and artificial iloy ` sections 'Llfand L3'. Line sections 4lected as indicated to 800 to 1400 cycles, is shifted to the position originally occupied by A, 200 to 800 cycles, by being modulated with 600 cycles and selectin the difference frequency band to the exc usion of the sum frequency band).

Similarly, the sub-band C is'shifted to the 800. to 1400 cycle position by being beaten with a carrier current of 600 cycles and the lower side band selected.` The sub-bands as thus shifted, B", C and A', are then col.-

l form the new telephone'band for transmission.

The arrangements forcarrying out the above described'method. of secretltransmission of messages may be understood more readily from referenceto Fig. 2 in which is shown a transmission line, includin the line 1 and L2 are balanced by networks N1 and N2, respectivel and include windings of the threewin ing transformers 1 and 2. InA transmitting from line L1, in which the voice frequency spectrum is normal, to line L2, in

which the frequency'spectrum is recast., the voice currents are divlded up by means of selective devices, such as filters F1, F, and F8, into individual circuits corresponding to the sub-bands A, B and C of the origlnal voice frequency band heretofore mentioned. In other words filter FB will transmit subband A of 200 to 800 cycles, filter F2 will transmit sub-bandB of 800 to 1400 cycles, and filter F1.will transmit sub-band C of 1400 to 2000 cycles. The sub-bands C and will be transmitted to themodulating dcvices M1 and M2 where they will be'modu- -latedby a current from source 19 of 600 cycles. The diierencey'in the; resultant frequency bands will then beselected in each case b theselective devices,\such as filters F4 an FWl In `other words filter F4 will transmit 800 to 1400 cyclesand filter F5 will transmit 200 to 800 cycles. The sub-band A `.will be 4 transmitted to the modulator M3 where it will'be modulated by a current from source 20`of 1200 cycles. The sum .term of modulation will then befselected out bythe filter F., which would be 1400 to 2000 cycles. The sub-bands. as rearranged in their new. frequency relation of B', A', willthen be recombined on circuit 4, and thence be transmitted out over line L2.r f v The recast and' unintelligible voice freuency spectrum' will: be transmitted over t e line L, to a distant station which will include apparatus similar -to that illustrated 1n Fig. 2 and to which reference will now be made. The recast and unintelligible voice frequency spectrum transmitted over line L2 wil be transmitted through transformer 2 and over circuit 5. Y' Associated with circuit 5 are the selective devices, such as filters F10, F11 and Fm which'will se varate the voice frequency band into ,the ysu -bands as rear ranged at .the distantfstation. For example vcurrent from source 19 of 600 cycles.

,filter Fw'will transmit sub-band C of 800 to 1400 cycles, filter F11 will transmit subband B. of 20010800 cycles, and filter F12 willf transmit sub-band Af of 1400 to 2000 cycles. Sub-bands C and B will ,thenbe transmitted tothe .demodulating devices M4 and M5 where they will befbeaten b ha e sum term of modulation will in each case be selectedoutby filters F7 and F8 which will restore the sub-bands C and' i3 to their ori inal frequency relation of 1400 to 2000 an 800 to 1400 cycles, respectively. Subband Awill be transmitted to`the modulating device M6 and will be beaten by ya currentffr'om'source 20-of 1200 cycles andthe difference selected out by filter F9, which will be 2,00. to 800 cycles, thereby restoring sub-band A. to its original frequency relation of A. The sub-bandsA, B and Care thus restored to their-normal frequency relation and when thus recombined on circuit. 6 are transmitted overline L1 to receiving ap aratus in intelligible form. l l

n Fig. 1 is illustrated in detail a form of modulating and deniodulating device M and the band filters F, which-elements have been l heretofore' referred to and illustrated sche-- matically in Fig. 2. The modulating and demodulating device M is shown as of the duplex vacuum bulb type', illustrated in the U. S. Patent No. 1,343,307 issued June 15,v 1920, to J. R. Carson. The band filters may be of the.types illustrated in the U. S. Patents Nos. 1,227,113 and 1,227,114 to George A. Campbell, although other selective'means might be-employed if desired. It is desirable to utilize the duplex type of vacuum bulb modulator for the followinglreasons: The carrier frequencies involved in forming the yfrequency shifting operation may be themselves in the telephone range of frequencies, in the case illustrated ybeing 600 cycles and 1200 y, cycles. These modulating` currents are prevented from being transmitted beyond the modulators by the'use of the duplex type of modulator circuit illustrat'edwhich suppresses by balance between the two tube output circuits, the component which remains unmodulated.. While this t `e of, modulating device is desirable it is pointed Vout "that it is not essential and that other types may. be employedl" important application of lsuch asecrecy system as has; been described is in aV radio tele hone transmission system, where because o the broad-cast nature of the usual radio transmission, it is especially desirable to renden unintelligible thetransmitted energy. Accordingly in Fig. 5l there has been illustrated anarrangement of the secrecy system of this invention as applied to a radio telephone transmission s stem. Similar reference characters have een used to denote likevparts in Figs. 2 and 5; The circuit arran ment of Fig. 5 is substantially similar to t at o fF ig. 2, the essential distinction being thatthe two one-way-'lbranchesof the secrecy-linen Fig` 2 are replacedji'n Fig.

'5 by a sending antenna 25 and a receiving antenna '26. yBetween the modulating and selecting portions of the secrecy vsystem and the respect-ive, antenna, there are provided radio frequency modulating devicesv M7 and Ms i and selective circuit elements, such as lters F13 and F14 whereby in sending, the

lrecast telephone frequency bandis stepped up to the radio frequency, and whereby, in receiving,- this band is stepped down from the radioto the audio frequency range. In-

terference with the incoming channel by the outgoing. channel is prevented by employing a'loop receiving antenna '26l balanced with respect-to transmitting antenna and by using where necessary or desired, differ# ent frequencies for sending and, receiving as generatedby '23 and 24 respectively. yAs in other res ectsthe arrangements and opera-4 tion oft e radiosystem of Fig. 5 are substantially the same as that already described withl respect to the arrangements of Fig. 2, no further description thereof will be given. In Fig. 4 `ofthe drawing is illustrated a case where the sub-bands A, B and C 'are not only shifted to diEerent positions in the frequency spectrum, but inbeing so shifted are also turned upside j down, las indicated by the dotted lines. This constitutes another element tendingto garble`and render unintelligiblethe telephone frequency band, particularly whenitiansmission of the imessage takes place over a wireline at telephone frequencies. The turning over of the subl bands is accomplished by so choosing the modulating frequency that the desired new position of a sub-band in the frequency 'range is represented by the component of mo ulation representing the difference between the sub-band and the modulating frequencies. There are required in the case il-., lustrated three modulating currents of different frequencies.' These modulating frequencies are illustrated as 2200 cycles for sub-band A', 1600 ccles for sub-band' B, and l' 2800 cycles for su -band C. These vmodu- 'lating frequencies are outside of the frequency ra of their respective sub-bands which facilitates excluding, by the4 use of selective circuits, the m0 ulating frequencies from interferingwith the transmission circuit proper. The circuit arrangements for carrying outvthe above outlined method p of changing the 'voice' frequency spectrum are substantially-similar to those already described andffurther description thereof will be omitteds It will be understood that the secrecy systemfof this invention is not. limited to any particular division of the voicefrequency range intsub-bands and furthermore the vspeech wave.

the incoming frequency band into su -and means iny each of saidftwo circuits for modulating frequencies may be varied. wide` ly. VVhile/in the cases illustrated the normal voice frequency range has been divided intothree. sub-bands of equal 'frequency ranges, these sub-bands may be of any de- I' kpended claims.

lhat is claimed is: 1. The method of transmitting messages secretly which `consists in dividing the original frequency band of the message into simultaneously existing sub-bands, shifting said sub-bands from. their normal positions in the frequency scale to produce a new' band having substantially the same width as the original signal band, transmitting said' sub-bands in ltheir shifted positions, and in restoring said shiftedsub-bands to their normal positions in the frequency scala Y 2. The-method of Isecret telephony whichv consists in; arbitraril dividing the speech wave yinto unintelligi le fragments, recom` bining said fragments' by modulation with i no other frequencies to form an unintelligible wave havingA substantiall wave, and transmitting said wave to a distant station, dividing said transmitted wave into its component 'fra nents, and, recombining said fragments y modulation with other frequencies to form saidv original 3. The Amethod ofsecret signaling which comprises dividing a' signal wave into its frequency components, recombining said components ,by modulation with other frequencies in an unintelli 'ble manner to pro! duce a wave having su antially the same width of .frequency range as the originalv signal wave, transmitting said componentsas recombined, and restoring said 4components by modulation with other frequencies 'at a receiving station to their original rela.- tion to form theoriginal si al wave.

' 4c. A transmission line inc uding two line sections, two one-way circuits transmittin Iin opposite. directions interconnecting saidl .lin'e sections, selective devices associated with each of said two circuits for seprating bands,

the same width` of frequency range as t e original signal for recombining said sub-bands to form saidv hand into sub-bands, means for modulating said sub-bands to alter their original frequency relation with respect to each other,

means for recombining said sub-'bands'in said altered relation to produce a Wave having substantially the saine Width. of frequency range as the original signal Wave, a plurality of selective devices at said receiving station for` separating said" recombined message band into its component sub-bands, means at" said receiving station, for modulating said sub-bands so as to restore said subbands to their original frequency relation ywith respect to each other, and means original message frequency band. 6. In' a system of signaling in which. sig-v nals are transmitted as modulated side' bands of a carrier current wave, the method of'at-4 taining secrecy `.which consists in transmitting a side band havin substantially the Same width` of range Ias t e ori ina-l message band', but with they individual requencies of the band rearranged l.with respectto their counterr'iarts` in the original banda y 7 rIna system of ysignaling in which si nalsare transmitted as' modulated side ban s of a. carrier current Wave, the method of at-` taining secrecy which consistsin transmittingI a side band having 'substantiallythe same width of range as the origina-l lmessage band,y but with the individual frequencies of the band rearranged with respect to their counterparts in the original band, demoduilating, the transmitted Waveat the receiving station, andv rearranging the components'of the'resultant signal wave so as to restore them to their original relation.

8. In asystem of signaling of the kind in which voice currents are transmitted as modulated side bands of a carrier current wave, the method of secret transmission Which comprises transmitting a side band which is substantially the same width of range as the original voice band', but with the individual frequencies rearranged with respect to their counter arts in the original voice band, demodulating the transmltted Wave at the receiving station, and rearranging the componentI frequencies of the resultant signal Wave to .produce a. Wave Vcorre-- spending to the'ori nal voice Wave.

9. The method 'on'transmission of waves representing a message having a band of frequency components occurring in a characteristic order, which comprises dividing said band into sub-bands, inverting the frequency order of the components Within certain sub-hands, recomhining said sub-bands in their altered condition to producea Wave transmitting said sub-*bands as recombined to a distant statlon.

10. The method of providing secrecy inv the transmission' of a message in-.a system of ycommunication which comprises dividing a yvoice frequency band into sub-bands, inverting the normal order of frequencies within -at` least one sub-hand, recomhining said sub-bands in their altered condition to produce a Wave Within the voice'v frequency range, and transmitting. all. of said subbands as recombined to a distant station.

11. The method of providingsecrecy'in the transmission of a message which comprises dividing a message frequency band into sub-bands, inverting the fre u'ency order ^Within at least one sub-band, s iiftingy at least one subsband'into a different position in the frequency scale with respect to the other sub-banda' iecombining said subbandsr in their altered condition and relation to produce a' wave having'substantially the same frequency Width as the oriv inal message'wave, land .transmitting all o the subebands as recombined to L a distant station.

12. The method ofl receiving a lband of frequencies representing a message in which certainy sublba'nds have the component frequencies in inverted order Which comprises restoring the' frequencies ofthe inverted sub-bands to the normal order and utilizing the restoredy sub-bands in connection with the other sub-bands to reproduce the message. i 13. A transmission line over which a inessage fre luency band is transmitted, a plurality o selective circuits assoc1ated with said line for dividing said message fre'- quency band into simultaneously existing sub-bands, means associated with said selective circuits for inverting the frequency order of the com onents Within certain'of said sub-bands, an means associated with said lastmentioned means for recombining said sub-bands in their altered condition to produce a band having substantially the same tially the same frequency width asy the original message band. n, l

'15. A 'transmission line over which a. message frequency band istransmitted, a plu-A rality .ofr selective circuits associated with said line for dividing said message frequency band into simultaneously existing subbands, means associated with said sey lective ycircuits for inverting the normal oi.-

de r of frequencies within at least one of said sub-bands, andmeans associated with said .selectivecircuits for recombining said sub-'bands in their altered condition to `produce a band having substantially the same frequency jwidth as the original message lband, and means for transmitting said last mentioned band to a distant station.

` 16. A transmission line over which a message Afreqi'iency band is transmitted, a plurality of selective circuits associated with said line -for dividing said. message fre- `quency band into simultaneously existing subba nds,means associated'with said selective circults for inverting the normal or- :der of frequencies `within at least 'one of said sub-bands, means associated withsaid selective 'circuits for shiftin at least one of said sub-bands into a di erent'position in thefrequency scale. with respect tothe other sub-bands,.mean's associated with said selective circuits for recombining said subbaiids in their altered condition and rela- 'tion to produce a band having substantially combining said sub-bands in their altered condition to produce a wave having substantially the same frequency width as the original message, and by transmitting said sub-bands las recombined, a receiving station comprisin a 'plurality of selective circuits for divi ing the-incoming unintelligible message band into sub-bands similar to the sub-bands asrecombined and trans` mitted out from 'the sending station, means in 'one of said selective circuits for rein-` selective circuits for dividing the original message frequency band into simultaneously existing sub-bands, means associated with said selective circuits for shifting certain of said sub-bands from their normal positions in the frequency scale, circuit means for recombining said sub-bands in their altered condition to produce anew band substan-v' tially no Wider than the original message frequency band, and means for transmitting said new band to a distant station, and a receiving station comprising a receiving circuit for said transmitted band, a plurality of selective circuits associated therewith for dividing said transmitted band into its component sub-bands, means associated with said selective circuits' for' shifting certain of said component sub-bands back. tov their original positions in the frequency scale, and circuit meansgfor recombining said sub-A bands as reshifted to form said original message frequency band. l

19. Inw a secret communication system, a sending station comprising a plurality of selective circuits for dividing the original message frequency band into simultaneousl n existing sub-bands, means associated wit said selective circuits forI shifting certain,

of said sub-bands from their normal positions in. the frequency scale, means associated with said selective circuits for inverting the normal order of frequencies Within certain of said sub-bands, means for recombining said sub-bands in 'their altered condition and relation to produce a new band substantially no wider than the ori nal message frequency band, and means or ltransmitting said new band to a distant station, and a receiving station comprising a receiving circuit for said transmitted' band, aplurality pf selective circuits associated therewith for dividing said transmitted band into itscomponent sub-bands, means associated with `said selective circuits for shifting certain of said component subbands back to their original positions in the frequency scale, means aociated with said selective circuits for reinverting the order of frequencies withincertain ,of said lsubmbands to restore them ,to normal, and circuit means for recombining said sub-bands as reshifted and reinverted to forni said original message frequency band. 20. A systeinof secret telephony comprising means for dividing tlie and of eech frequency components into sub-ban s .of frequency componenta'means for chan ng a characteristicof at least one sub-ban so Ythat when it is recombined with the other sub-bands the intelli 'bility of the tant lwave is material combining the' sub-banI s into a band of such reduced intelli 'bility and 'of approximately the same wi th as the original band, and a circuit for transmitting the wave so produced.. p f

21. The method of transmitting with crecy a message represented by 'waves llaving a band of frequencies occurrin in a characteristic order, comprising dividing v1.20 reduced, means for 5 q'ueney components is changed to 'educe the nixelligibiity of the resulting bandi., and transmitting the altered band of frequency components, y r

The method of semefr telephony i@omm 10 grsin'g dividing speech 'Waves into subzmds each of to@ Smau a, f'equency fange fio be readily understandable, altering the requency relations of the frequency componens of certain. of. the sub-bans to mnke the sub-bends stil' ese understaxmdzhle, recombining 'the altered subbnnds to ferm af wave having substantially the' same frequency width as the original speech band, and transmibting the recombined subfbanc'ls l to a distance.

In testimony wheeof, I have sigfnedl my neme to this specifeetion this'7th day of January 1920.

LLOYDy ESPENSGHIED. 

